1. Field of the Invention
The present invention relates to a distance measurement device, for example, to be mounted on a vehicle, for measuring a distance from the vehicle to an object ahead of the vehicle.
2. Description of Related Art
As a distance measurement device of this type in related art, there is known one that calculates the distance from a vehicle to an object ahead of the vehicle, for example, having two pieces of cameras that are both arranged facing towards ahead of the vehicle with their optical axes being separated from each other by a predetermined distance, based on parallax information of images obtained from the respective cameras. Such a distance measurement device is used in a system, for example, for detecting an inter-vehicle distance and/or sensing an obstacle ahead of the vehicle.
It will be appreciated that, in general, the accuracy of distance measurement relies on the accuracy of alignment of two cameras. Accordingly, when the distance between the two cameras is changed or when the optical axis of one of the cameras is shifted from a predetermined direction, there has been a problem in that the accuracy of distance measurement is deteriorated.
In an attempt to solve this problem, for example, a vehicle mounting camera has been disclosed in Japanese Patent Laid-Open Publication No. 2001-88623. FIG. 4 shows the conceptual structure of such a vehicle mounting camera 21 in related art.
As shown in FIG. 4, the vehicle mounting camera 21 disclosed in Japanese Patent Laid-Open Publication No. 2001-88623 has a pair of cameras 22 and 23, a camera stay 24 for holding the cameras 22 and 23 in predetermined positions, and an installation section 25 in a unified structure with the camera stay 24 to be secured to a housing 26 of a vehicle. The vehicle mounting camera 21 is adapted to accurately maintain the relative positions of the cameras 22 and 23 with respect to each other by being tightly secured to mounting holes 30, 31 and 32 provided on the housing 26 of the vehicle by three screws through three mounting holes 27, 28 and 29 provided in the installation section 25.